1. Field of the Invention
The present invention relates to surge voltage arresters, and more particularly to such voltage arresters having concentrically arranged electrodes.
2. The Prior Art
A surge arrester of the type having two concentrically arranged electrodes separated by a discharge space, and insulated from each other by a hollow cylindrical insulating body located outside the discharge space is illustrated and described in U.S. Pat. No. 3,651,380. In a surge arrester of this type, the response voltage rises in response to the steepness of the waveform of the voltage applied across the surge arrester. The hollow space within the arrester is filled with gas, which is a very good insulator in its unfired state, and accordingly ions must be formed within the gas before a conducting plasma can be created. Because of the time required for ionization of the gas-discharge section, there is a delay in firing the surge arrester, which results in an operation in which the arrester fires at a higher voltage level for a steeply rising voltage than for an applied voltage which rises at a lesser rate.
Various ways of combating the ionization delay have been proposed in the past. In the case of so-called button arresters, a conductive trigger line has been placed on the insulating wall which defines the discharge space, as described in U.S. Pat. No. 3,979,646. In the button arresters, the two electrodes are placed symmetrically opposite each other in a tubular insulating body which defines and surrounds the discharge space. While this technique is effective in the case of button arresters, the ionization delay problem is more difficult in arresters which have electrode structures which are concentrically aligned, because there is then no insulating body which defines a part of the discharge space.
A reduction in the operating voltage can be achieved by the use of radioactive material in either solid or gaseous form. The radiation from the radioactive material causes some ionization of the gas, which reduces the time required to ionize the gas sufficiently to form a conductive plasma. This process has disadvantages, however, among which are the decreasing activity of the radioactive material with time, and a reluctance on the part of some users to use surge arresters with substantial amounts of radioactive material.
Applicants have found that on poorly conductive insulators, a stationary wall charge is formed which induces the countervoltage by means of electrostatic charges, which countervoltage works against a rapid operation of the surge voltage arrester. By neutralizing the countervoltage, applicants have found that it is possible to increase the firing speed of the arrester.